This is a fascinating thread and something I'm really grateful for as comp titles are my Achilles heel (along with elevator pitches, synopses... How many heels do I have? 😂 )
I get why comp titles exist - they're a short hand, a way to give an agent a flavour of your story and a way for the agent to see how savvy the writer is, if they know their own story and how it sits in the market.
However, from my (granted comparatively limited) experience, it seems comp titles are pretty much compulsory for American agents and not necessarily so for British ones.
For example, when I took part in a pitching event on Twitter, the feedback I had was generally great but my submission was criticised for not including comp titles, despite not specifically being asked for them (all those involved were American, btw)
But while subbing to UK agents, I haven't come across many agencies that ask for them - some, yes, but they're definitely in the minority.
Has anyone else had experience of this? Is there a heavier emphasis on comp titles with American agents over UK ones?